1. Field of the Invention
The present invention generally relates to a device that continuously equalizes the charge state of a battery, e.g., a lithium ion battery, and a control algorithm implemented using the device.
2. Description of the Related Art
There is a continual need for miniaturization of spacecraft electronics to reduce mass, power and assembly cost. While this need extends to all spacecraft systems, substantial benefits can be had by using common spacecraft subsystems that can be easily reused among multiple spacecraft with a minimum amount of reconfiguration. Once such subsystem is lithium ion (Li-Ion) battery charger. However, Li-Ion battery cells, even from a common production lot, do not have perfectly matched parameters such as capacity and cell impedance, for example. As a result, individual cell charge states diverge, especially over multiple charge cycles, and, since the overall capacity of the Li-Ion battery is limited by the cell having the lowest charge state, significant portions of the battery capacity are forfeited. Traditional end-of-charge cell balancing techniques are based on reacting to the cell with the highest potential, resulting in a majority of the cells not being at the maximum charge state. Thus, traditional systems cannot simultaneously establish maximum charge states for all cells in a battery.
Accordingly, there is an ongoing need for improved battery charging devices and control algorithms for the same.